This invention relates to a process for producing an aqueous solution of a particulate material having a fine particle size, typically a polymeric particulate material, which is difficult-to-dissolve in water.
The polymeric particulate materials of this invention, such as polyacrylamide, which have a small particle size are very slippery when wetted. This is even more pronounced in materials which have an extremely fine particle size (50 micron or less). Therefore, any spillage or airborne dry polymeric dust due to the use of an "open" system migrates onto areas such as floors, stairways and handrails of a manufacturing facility potentially becoming a great hazard to workers when they become wetted.
Since there are no closed systems for producing solutions of fine micron size versions of the above-described polymers, coarser polymeric particulate materials having much higher relative particle size (250 microns or more) are instead employed in producing solutions of these hard-to-dissolve polymers. A problem associated with these coarser polymeric particulate materials is, however, the length of time it takes them to dissolve them and form a solution. In the formation of polyacrylamide solutions, for example, the intertwined higher molecular weight polymeric chains of the coarser polymeric materials become untangled over time, upon "aging" in water, as the solution reaches its full potency. This aging process requires large tanks for mixing and storing polymer solutions before they can actually be used. Accordingly, the need for including the above-described aging step in the overall solution formation process results in the need for a more costly and a more time consuming manufacturing system in order to produce an aqueous solution in which the polyacrylamide particulate material is substantially completely dissolved.
Complex formation apparatus for forming solutions of the coarser subject materials has also been produced. In U.S. Pat. No. 3,738,534, a vortex chamber is used to provide a hollow cylindrical rapidly flowing film of fluid onto the inner surface of which the polymeric material is introduced. The apparatus of U.S. Pat. No. 3,893,655 includes a vertically mounted wetted wall funnel having a throat of reduced cross-section at the bottom. The particulate solid material is distributed onto the interior surface of the wetted wall funnel and the solids-liquid mixture withdrawn from the funnel and admixed into the liquid flowing past the throat of the funnel. In U.S. Pat. No. 4,518,261, the vessel 201 and the water supply pipe 202 are so constituted that water is whirled within the vessel about the discharge pipe. The water whirled within the circular division plate 205 and discharged from a funnel-shaped discharge pipe 204. The energy and flowing conditions of the water which is whirled while generating negative pressure and discharged from the discharge pipe 204 is normally sufficient to disperse the polymer powder in the water. A particle size reduction apparatus is shown in U.S. Pat. No. 4,529,794, in which a suspension of polymer particles is formed and subjected to conditions of high shear in order to force the particles into solution. The pumping action of an impeller rotating at 10,000 to 13,000 rpm reduces the size of, and dissolves, the polymer particles. In another high shear apparatus described in U.S. Pat. No. 4,603,156, the polymer particles are first comminuted, and the comminuted material and water are fed to a mechanical dispersion means 16. The dispersion means comprises a boxlike housing having an open bottom side, and impeller/stator assembly mounted in the housing. In U.S. Pat. No. 4,778,280, a mixing apparatus is provided having a first centrifugal pump including a casing and an impeller located therein. The casing has an axially extending tubular inlet located centrally on its end wall. The discharge comprises a tubular projection on the sidewall's casing. A second centrifugal pump includes a casing which is substantially identical to the casing of the first pump. The second casing has a tubular projection on its end wall. The water is delivered to one end wall of the second casing. The polymer is directed to the other end wall of the second casing. The swirling water in the second casing creates a lower pressure at its discharge to draw the polymer downwardly and into the first casing where it is mixed with the incoming water.
Therefore a need exists for a process for producing an aqueous solution of a difficult-to-dissolve, fine particle size particulate material, typically a polymeric particulate material, wherein aging time is substantially reduced and in which spillage or airborne dry polymeric dust is eliminated.